Introduction

MIS technique compared to the open technique is associated with substantial benefits for the patients, attributable to less surgical trauma; however, this does not imply the absence of physiologic changes when not anticipated may be deleterious. These physiologic alterations are triggered by a combination of the following: the insufflation gas used, the increase in intra-abdominal pressure (IAP), the extreme patient positioning during surgery, and the effect of the surgery itself [1].

Carbon Dioxide (CO2) Effect

Carbon dioxide is the gas of choice used for insufflation in MIS, as it is nontoxic, nonflammable, rapidly soluble in blood, easily eliminated by the lungs, and relatively inexpensive [1]. Since CO2 is a normal product of cellular metabolism, at physiological levels is nontoxic and an efficient means for its elimination is inherent in humans.

The absorption rate of CO2 is influenced by its partial pressure gradient between the cavity and the blood, its diffusion coefficient, the surface area of the cavity, and the perfusion of the walls of the cavity [2]. The CO2 absorbed is dissolved in the blood and delivered to the lungs for excretion by ventilation, while the majority combines with water to form carbonic acid, which dissociates into hydrogen and bicarbonate. The hydrogen ions complex with hemoglobin and the bicarbonate diffuses into the plasma. These result in an increase in arterial pCO2 and a fall in arterial pH.

The space insufflated with CO2 influences the physiologic changes exerted by CO2 absorption. Intraperitoneal insufflation with CO2 is associated with an initial rapid rise in pCO2 during the first 15 min and followed by plateau or second phase of slower change [2]. Extraperitoneal insufflation shows a significantly faster rise in pCO2 and tends to persist into the postoperative period [3]. The magnitude of the rise in pCO2 was not significantly different between extra- and intraperitoneal insufflation [2]. The faster rate seen in extraperitoneal insufflation may be due to concentrated absorption, vascularity of the extraperitoneal space, a faster diffusion in the extraperitoneal cavity, or a combination of these factors.

Mild hypercarbia (pCO2 of 45–50 mm Hg) has minimal effect on hemodynamics; however, moderate to severe hypercarbia have both direct and indirect effects on the cardiovascular system: direct effects include myocardial depression and vasodilatation, while indirect effects are brought about by catecholamine release eventually causing increase myocardial oxygen consumption [2]. While most healthy individuals will not be significantly affected by CO2 elevation and can be corrected with moderate hyperventilation; those with cardiorespiratory compromise may not respond similarly and will need careful perioperative monitoring.

Insufflation with CO2 results in a blunted immune response compared to open procedures. Acute-phase reactant (C-reactive protein) and cytokines (interleukin-6 and tumor necrosis factor-alpha) produced in response to tissue injury are likewise reduced in the presence of CO2 [4].

Pneumoperitoneum/Increase Intra-abdominal Pressure Effect

Insufflation of the abdominal cavity results in shifting the abdominal wall outwards and the diaphragm upwards, resulting in an increase in intra-abdominal pressure (IAP) and reduction of thoracic volume, respectively. Respiratory compliance is reduced by 50% when the peritoneal cavity is insufflated to a pressure of 15 mm Hg [1, 5]. Pulmonary functions reduced with the decrease in lung compliance include forced expiratory volume in the first second (FEV1), functional residual capacity (FRC), total lung capacity, and vital capacity (VC) [1]; these changes can predispose to the development of ventilation-perfusion mismatch, leading to hypoxemia. Increasing the ventilatory rate is necessary to promote ventilation and maintain pCO2 at or near-normal levels (Fig. 1).

Fig. 1
An illustration of a patient reclining on a table with an inflatable tube in their abdomen. Arrows are located within, two indicate to the abdominal wall and four point to the left side. Four arrows on the inner lining of the organs, below the liver, all point inward toward the large blood veins.

Effects of increased intra-abdominal pressure on organs

Full size image

Hemodynamic changes seen with pneumoperitoneum are the result of mechanical and neurohormonal responses. The increased IAP caused by pneumoperitoneum produces vascular compression of the inferior vena cava (IVC), aorta, splanchnic vasculature, and renal vasculature; this shifts the peripheral vascular volume to the central venous compartment, causing an initial increase in venous return [5]. A biphasic response is seen with an increase in the right atrial pressure (RAP), left atrial pressure (LAP), and cardiac output (CO) at 7.5 mm Hg IAP; as the IAP increases beyond 15 mm Hg, both the RAP and LAP remain elevated however the CO starts to decrease below the baseline [6]. The drop in CO is attributed to the decreased venous return caused by IVC compression and the pooling of the venous blood in the lower extremities. There is also an increase in afterload with an increase in IAP, seen as an increase in mean arterial pressure (MAP) and systemic vascular resistance (SVR) that contribute to the decrease in CO. The compression of the renal vasculature reduces renal blood flow stimulating the release of aldosterone and renin that contribute to the increase in MAP, and the release of atrial natriuretic peptide cortisol, epinephrine, norepinephrine, and vasopressin.

The hemodynamic changes will immediately return to baseline levels after desufflation among healthy individuals, in those with cardiovascular disease these can persist for at least 65 min. Those with cardiovascular compromise may experience an elevation in cardiac index, ejection fraction, heart rate, left ventricular stroke work index, and decrease in SVR; with 20% of these patients developing heart failure within 3 h after the MIS procedure [7]. Though laparoscopy appears to be safe in patients with cardiac disease, it will require special attention and additional intraoperative monitoring.

Patient Positioning Effects

Placing the patient in Trendelenburg or reverse Trendelenburg position facilitates optimal visualization of the surgical field in the lower abdomen or pelvis and the upper abdomen, respectively. Shifting from supine to Trendelenburg position displaces the diaphragm and abdominal contents cephalad. This enhances the pulmonary compromise associated with CO2 insufflation, reduction of pulmonary compliance, and increase peak airway pressure. It however mitigates the effect on the hemodynamic changes with increased venous return and pulmonary capillary wedge pressure which minimize the decline in CO with an increase in IAP [5]. The reverse Trendelenburg position will generate positive ventilatory effects and negative hemodynamic effects.

Summary

The MIS technique imposes physiologic changes outside of that caused by anesthesia and the nature of surgery; these factors include CO2 use, increase IAP, and patient positioning. These pulmonary and cardiovascular changes are generally well tolerated by the healthy patient during the procedure and recover immediately afterward. Cognizance of intraoperative and sustained effects afterward among patients with cardio-pulmonary impairment would emphasize the need for thorough preoperative preparation and vigilant perioperative monitoring to mitigate the adverse effects.